Servo-controlled manual gear changes are increasingly widespread and, from a structural point of view, are entirely similar to a conventional manual gear change except for the fact that the control pedals and levers that can be actuated by the driver are replaced by corresponding electrical or hydraulic servo-controls. When using a servo-controlled manual gear change, the driver merely has to send a command to a control unit to change to a higher or a lower gear and the control unit independently performs the gear change by acting on the control of the butterfly valve and on the various servo-controls.
In normal driving conditions using a servo-controlled gear change, it is necessary to ensure a high level of comfort for passengers during the gear change stages; recent studies have shown that in order to ensure a high level of comfort for passengers it is necessary for the gear change to be performed rapidly without triggering oscillations likely to be noticed by the passengers.
It is known that the time duration of the gear change is determined largely by the synchronisation time of the new gear, i.e. by the time taken by the synchronisers to match the angular speed of the primary shaft of the gear change to the angular speed imposed by the new ratio.
In order to reduce the synchronisation time during the gear progression, i.e. during a change from a lower to a higher gear, it has been proposed to use a braking device coupled to the primary shaft of the gear change in order to brake the primary shaft and rapidly to match the angular speed of the primary shaft to the angular speed imposed by the new ratio. This solution is relatively costly and complicated, however, because it is necessary to provide and control a brake coupled to the primary shaft of the gear change.